Method and apparatus for mapping/demapping resource in wireless communication system

ABSTRACT

A method and apparatus for mapping/demapping a resource efficiently in a wireless communication system are provided. A resource mapping method of a transmitter in a wireless communication system includes precoding pairs of symbols, arranging the pairs of precoded symbols adjacently in a resource block, and transmitting the pairs of precoded symbols in the resource block.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on Jan. 8, 2010 in the Korean IntellectualProperty Office and assigned Serial No. 10-2010-0001596, and of a Koreanpatent application filed on Sep. 29, 2010 in the Korean IntellectualProperty Office and assigned Serial No. 10-2010-0094810, the entiredisclosures of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications. Moreparticularly, the present invention relates to a method and apparatusfor mapping/demapping resources efficiently in a wireless communicationsystem.

2. Description of the Related Art

Most of the evolved 3rd generation wireless communication systems,including 3rd Generation Partnership Project (3GPP) Long Term Evolution(LTE), 3GPP LTE-Advanced (LTE-A), and Institute of Electrical andElectronics Engineers (IEEE) 802.16m, have adopted Orthogonal FrequencyDivision Multiplexing (Multiple Access) (OFDM(A)) as a multi-carriermultiple access scheme.

In the downlink of a wireless communication system adoptingmulti-carrier multiple access, a base station (e.g., evolved Node B(eNB)) allocates resources to a terminal (e.g., User Equipment (UE) andMobile station (MS)) for data transmission in units of a Resource Block(RB) which is composed of a plurality of subcarriers and a plurality ofOFDM symbols.

In transmission, the base station can use spatial multiplexing andtransmission diversity. In a 3GPP LTE or LTE-A system, transmissiondiversity includes applying precoding to codewords mapped to individuallayers and mapping the precoded codewords to the Resource Elements (REs)of the RBs allocated to the corresponding terminals. In the 3GPP LTE-Asystem, a Demodulation Reference Signal (DM-RS), for demodulating, atthe UEs, the received signal, and a Channel State Information ReferenceSignal (CSI-RS), for measuring the channel state, are introduced.However, these reference signals are not being used in the 3GPP LTEsystem. With the introduction of the DM-RS and CSI-RS, the resourcelocations for data transmission are changed as compared to theconventional LTE system and, as a consequence, the precoding andresource mapping designed for use in the LTE system for transmissiondiversity cannot be applied to the LTE-A system without performancedegradation.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly an aspect of the presentinvention is to provide a resource mapping/demapping method andapparatus that is capable of overcoming the decoding performancedegradation problem caused by precoded paired symbols that are mapped toresource elements positioned far apart from each other in a resourceblock.

In accordance with an aspect of the present invention, a resourcemapping method of a transmitter in a wireless communication system isprovided. The method includes precoding pairs of symbols, arranging thepairs of precoded symbols adjacently in a resource block, andtransmitting the pairs of precoded symbols in the resource block.

In accordance with another aspect of the present invention, a resourcedemapping method of a receiver in a wireless communication system isprovided. The method includes demapping, when a signal is received,pairs of precoded symbols in a resource block assigned to the receiveraccording to a mapping rule, the precoded symbols being arrangedadjacently in the resource block, and decoding the pairs of precodedsymbols according to a paired symbol precoding scheme.

In accordance with another aspect of the present invention, a resourcemapping apparatus of a transmitter in a wireless communication system isprovided. The apparatus includes a precoding pair selector for selectingpairs of symbols, a precoder for precoding the selected pairs ofsymbols, a resource element mapper for arranging the pairs of precodedsymbols in a resource block, and an Orthogonal Frequency DivisionMultiplexing (OFDM) symbol generator for performing OFDM modulation onthe arranged pairs of symbols and for transmitting the OFDM symbolsthrough antennas.

In accordance with still another aspect of the present invention, aresource demapping apparatus of a receiver in a wireless communicationsystem is provided. The apparatus includes a resource element demapperfor demapping, when a signal is received, pairs of precoded symbols in aresource block assigned to the receiver according to a mapping rule, theprecoded symbols being arranged adjacently in the resource block, and asymbol decoder for decoding the pairs of precoded symbols according to apaired symbol precoding scheme.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following description inconjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating arrangements of common referencesignals for use in a Long Term Evolution (LTE) system according to anexemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating arrangements of Demodulation ReferenceSignals (DM-RS) for use in an LTE-Advanced (LTE-A) system according toan exemplary embodiment of the present invention;

FIGS. 3 and 4 are diagrams illustrating arrangements of precoded symbolsmapped to Resource Elements (REs) in a communication system according tothe related art;

FIGS. 5 to 11 are diagrams illustrating a principle of a method formapping precoded symbol pairs to resource elements according to a firstexemplary embodiment of the present invention;

FIGS. 12 and 13 are diagrams illustrating arrangements of precodedsymbols mapped to REs in Resource Blocks (RBs) according to a secondexemplary embodiment of the present invention;

FIG. 14 is a block diagram illustrating a configuration of a transmitteraccording to an exemplary embodiment of the present invention;

FIG. 15 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment of the present invention;

FIG. 16 is a flowchart illustrating a resource element mapping method ofa transmitter according to an exemplary embodiment of the presentinvention;

FIG. 17 is a flowchart illustrating a resource element demapping methodof a receiver according to an exemplary embodiment of the presentinvention;

FIG. 18 is a diagram illustrating arrangements of channel stateinformation reference signals in resource blocks used in an LTE systemaccording to an exemplary embodiment of the present invention;

FIG. 19 is a diagram illustrating a principle of precoded paired symbolmapping in an LTE system according to an exemplary embodiment of thepresent invention;

FIG. 20 is a diagram illustrating exemplary arrangements of precodedpaired symbols when the number of Common Reference Signal (CRS) antennaports is 2 and the number of Channel State Information Reference Signal(CSI-RS) antenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 21 is a diagram illustrating exemplary arrangements of precodedpaired symbols when the number of CRS antenna ports is 2 and the numberof CSI-RS antenna ports is 2 in an LTE-A system according to anexemplary embodiment of the present invention;

FIG. 22 is a diagram illustrating exemplary arrangements of precodedpaired symbols when the number of CRS antenna ports is 4 and the numberof CSI-RS antenna ports is 1 in an LTE-A system according to anexemplary embodiment of the present invention;

FIG. 23 is a diagram illustrating exemplary arrangements of precodedpaired symbols when the number of CRS antenna ports is 4 and the numberof CSI-RS antenna ports is 2 in an LTE-A system according to anexemplary embodiment of the present invention;

FIG. 24 is a diagram illustrating an arrangement of precoded pairedsymbols when the number of CRS antenna ports is 2 and the number ofCSI-RS antenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 25 is a diagram illustrating arrangements of precoded pairedsymbols when the number of CRS antenna ports is 2 and the number ofCSI-RS antenna ports is 2 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 26 is a diagram illustrating arrangements of precoded pairedsymbols when the number of CRS antenna ports is 4 and the number ofCSI-RS antenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 27 is a diagram illustrating arrangements of precoded pairedsymbols when the number of CRS antenna ports is 4 and the number ofCSI-RS antenna ports is 2 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 28 is a diagram illustrating an arrangement of non-precoded symbolswhen the number of CRS antenna ports is 2 and the number of CSI-RSantenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 29 is a diagram illustrating an arrangement of non-precoded symbolswhen the number of CRS antenna ports is 2 and the number of CSI-RSantenna ports is 2 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 30 is a diagram illustrating an arrangement of non-precoded symbolswhen the number of CRS antenna ports is 4 and the number of CSI-RSantenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention;

FIG. 31 is a diagram illustrating an arrangement of non-precoded symbolswhen the number of CRS antenna ports is 4 and the number of CSI-RSantenna ports is 2 in an LTE-A system according to an exemplaryembodiment of the present invention; and

FIG. 32 is a diagram illustrating an arrangement of inter-OFDM-precodedsymbols in an LTE-A system according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

Transmission diversity is a technique used to improve receptionperformance by transmitting a signal on multiple channels to overcomemultipath fading.

In a Long Term Evolution (LTE) system, Space Frequency Block Coding(SFBC) and Frequency Switched Transmit Diversity (FSTD) are used astransmission diversity techniques. In order to apply theses transmissiondiversity techniques, modulation symbols are assigned to each layer andprecoded for transmission diversity, and then precoded symbols aremapped to resource elements. The precoded symbols are mapped to resourceelements that are not occupied by a Physical Broadcast Channel (PBCH), aSynchronization signal, a Reference Signal, or a Physical DownlinkControl Channel (PDCCH) of the resource block assigned to thecorresponding User Equipment (UE). The precoded symbols are mapped infrequency-preferable order, i.e., from the first subcarrier of the firstOrthogonal Frequency Division Multiplexing (OFDM) symbol in frequencydirection and, if the resource of the first OFDM symbols are completelyassigned, then from the first subcarrier of the resource block of thenext OFDM symbol.

In an LTE-Advanced (LTE-A) system, positions of resource elements fortransmitting LTE-A data due to the newly introduced DM-RS are differentas compared to the LTE system. Accordingly, in case that the precodingand resource mapping designed for achieving the transmission diversityin the LTE system are applied to the LTE-A system without modification,the transmission performance degrades. The reason of the performancedegradation is discussed herein.

As aforementioned, the 3^(rd) Generation Partnership Project (3GPP) LTEsystem uses the SFBC and FSTD for transmission diversity under theassumption that 2 or 4 transmission antennas are used.

The SFBC is a frequency axis type of Space Time Block Code (STBC) whichis also known as an Alamouti code. The SFBC is composed of orthogonaltransmission diversion streams and designed to obtain optimum Signal toNoise Ratio (SNR) at a linear receiver. Such an orthogonal code existsonly with two transmission antennas. In the LTE system, the SFBCtransmission is configured as equation (1) such that the symbols aretransmitted on a pair of adjacent subcarriers through two antenna ports.

$\begin{matrix}{\begin{bmatrix}{y^{(0)}(1)} & {y^{(0)}(2)} \\{y^{(1)}(1)} & {y^{(1)}(2)}\end{bmatrix} = \begin{bmatrix}x_{1} & x_{2} \\{- x_{2}^{*}} & x_{1}^{*}\end{bmatrix}} & (1)\end{matrix}$

In equation (1), y^((p))(k) denotes the symbol transmitted on the k^(th)subcarrier at the p^(th) antenna port.

The orthogonal code used in the SFBC does not exist for an antennaconfiguration higher than 2×2. In an LTE system using 4 transmissionantennas, SFBC and FSTD are used in combination as shown in equation(2):

$\begin{matrix}{\begin{bmatrix}{y^{(0)}(1)} & {y^{(0)}(2)} & {y^{(0)}(3)} & {y^{(0)}(4)} \\{y^{(1)}(1)} & {y^{(1)}(2)} & {y^{(1)}(3)} & {y^{(1)}(4)} \\{y^{(2)}(1)} & {y^{(2)}(2)} & {y^{(2)}(3)} & {y^{(2)}(4)} \\{y^{(3)}(1)} & {y^{(3)}(2)} & {y^{(3)}(3)} & {y^{(3)}(4)}\end{bmatrix} = \begin{bmatrix}x_{1} & x_{2} & 0 & 0 \\0 & 0 & x_{3} & x_{4} \\{- x_{2}^{*}} & x_{1}^{*} & 0 & 0 \\0 & 0 & {- x_{4}^{*}} & x_{3}^{*}\end{bmatrix}} & (2)\end{matrix}$

In order to demodulate in the wireless communication system, it isnecessary to estimate the channel environment which the received signalhas experienced. In 3GPP LTE and LTE-A, a Common Reference Signal (CRS)and a Demodulation Reference Signal (DM-RS) are used for this purpose.

FIG. 1 is a diagram illustrating arrangements of common referencesignals for use in an LTE system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 1, the CRS is a reference signal transmitted to allUEs within the cell of a corresponding evolved Node B (eNB) in an LTEsystem. The CRS is used for creating channel state information anddemodulating the received signal. As shown in parts (a), (b), and (c) ofFIG. 1, the Resource Blocks (RBs) are designed differently depending onthe number of antenna ports, and each RB includes the Resource Elements(REs) carrying the CRSs.

FIG. 2 is a diagram illustrating arrangements of Demodulation ReferenceSignals (DM-RS) for use in an LTE-A system according to an exemplaryembodiment of the present invention.

Referring to FIG. 2, the DM-RS is transmitted as precoded per resourceblock in separation from the channel state information demodulationsignal and distinguished between transmission layers so as to be capableof being used with multiple antennas and demodulated by the UE assignedthe corresponding resource block and corresponding layer transmission.The DM-RS is used to demodulate the received signal. Parts (a) and (b)of FIG. 2 show the RBs for different numbers of antenna ports, and eachresource block includes the REs carrying the DM-RSs.

As shown in FIGS. 1 and 2, the change of the positions of the REscarrying the CRS and DM-RS causes the change of the REs carrying data onthe PDCCH in the LTE and LTE-A systems.

A description is made of the arrangement of REs carrying the precodedsymbols hereinafter.

In the LTE system, the modulation symbols are precoded and then mappedto the REs of the RB assigned to a corresponding UE. At this time, theprecoded symbols are mapped to the REs of the RB according to thefollowing rules.

First, the precoded symbols are not mapped to RBs carrying a PBCH, asynchronization signal, or a reference signal.

Second, the precoded symbols are not mapped to OFDM symbols of a controlchannel such as a PDCCH.

Under these rule, the resource allocation is performed starting from thesubcarrier having the lowest index in the first OFDM symbol byincrementing the subcarrier index. If reaching the subcarrier with lastindex in the assigned RB, the resource allocation restarts from thesubcarrier with lowest index in the next OFDM symbol. That is, theresource allocation is performed in units of RE from bottom to top andfrom left to right.

In the LTE system, the precoded symbols are mapped to an RB infrequency-preferable order as described above.

FIGS. 3 and 4 are diagrams illustrating arrangements of precoded symbolsmapped to REs in a communication system according to the related art.

Referring to FIGS. 3 and 4, the precoded symbols are mapped to the REsin the aforementioned process. In the example of FIGS. 3 and 4, it isassumed that the RB assigned to the receiver is composed of nsubcarriers. For simplicity, the subcarriers are indexed with 0 to n−1from bottom to top such that the precoded symbols are mapped in thisorder in the RB. Also, the OFDM symbols are indexed in order of m andm+1 from left to right such that the precoded symbols are mapped in thisorder.

In the LTE system, transmission diversity is based on the SFBC.Accordingly, in order to apply transmission diversity, the number ofprecoded symbols must be twice the number of REs. Also, according to thebasic assumption for applying the SFBC, the paired symbols have toexperience the same or very similar channel environments. Accordingly,it is preferred to map the paired symbol to the adjacent REs. Part (a)of FIG. 3 shows an exemplary case where the paired symbols are arrangedin an OFDM symbol carrying CRS. In more detail, the precoded symbols aremapped to the REs in order, avoiding the subcarriers (indexed by 0, 3,6, 9, . . . , n−12, n−9, n−6, and n−3) carrying the CRSs, in the secondOFDM symbol indexed by m+1. The dotted lines and solid lines indicatepairing of the precoded symbols. In this manner, the LTE system arrangesthe SFBC-precoded paired symbols on the adjacent subcarriers.

Although the CRS of the LTE system is still used, a new referencesignal, i.e. DM-RS, is introduced in the LTE-A system. With the use ofthe new reference signal, the transmission diversity and resourcemapping designed for the LTE system cannot be applied to the LTE-Asystem without degradation of demodulation performance. This is becausethe number of empty REs that can be mapped to the precoded symbols is anodd number in one OFDM symbol. A more detailed description is madeherein with reference to parts (b), (c), and (d) of FIG. 3.

Parts (b) and (c) of FIG. 3 show exemplary cases of an LTE-A system inwhich the precoded symbols are mapped to available REs in the samemanner as the LTE system when a number of resource blocks is odd andeven, and with the number of antenna ports being less than or equal to2. Part (d) of FIG. 3 shows an exemplary case of precoded symbols mappedto available REs in the same manner as the LTE system when a number ofantenna ports is equal to or less than 3. Here, the SFBC precoded pairedsymbols are connected through solid or dotted lines.

In case that an odd number of RBs is assigned, when the SFBC-precodedsymbols are mapped in the same manner as the LTE system, theSFBC-precoded symbol arranged on the last available subcarrier in thefirst OFDM symbol carrying the DM-RSs is paired with the SFBC-precodedsymbol arranged on the first available subcarrier in the following-OFDMsymbol carrying the DM-RSs, resulting in difficulty of correctdemodulation. As shown in part (b) of FIG. 3, the paired symbols mappedto the RE (m, n−2) defined on the second last subcarrier in the firstOFDM symbol and the RE (m+1, 0) on the first subcarrier in the secondOFDM symbol are likely to incur an error in demodulation process. Thetwo paired symbols are connected through a dotted line.

Meanwhile, even though there is an even number of empty REs in the OFDMcarrying the DM-RSs, if the empty REs are continuous and the number ofempty REs is not a square of 2 as in the case where two resource blocksare assigned or the number of antenna ports is three, the paired symbolsare spaced apart by as many as 1 or more subcarriers on the frequencyaxis, resulting in degradation of SFBC demodulation performance. Thisproblem occurs regardless of the number of assigned resource blocks orthe number of antenna ports. The RE pair {(m, 0), (m, 2)} in part (a) ofFIG. 3, the RE pairs {(m, 0), (m, 2)} and {(m+1, 0), (m+1, 2)} in part(c) of FIG. 3, and the RE pairs {(m, 4), (m, 7)} and {(m+1, 4), (m+1,7)} in part (d) of FIG. 3 are the representative examples.

As aforementioned, the reason why the performance degradation of thetransmission diversity occurs in the LTE-A system is because theSFBC-precoded paired symbols are not arranged on adjacent resourceelements due to the newly introduced DM-RS.

A description is made of a method for arranging precoded paired symbolsaccording to an exemplary embodiment of the present inventionhereinafter.

According to exemplary embodiments of the present invention, twoapproaches are proposed to address the aforementioned problem. The firstis to reselect the precoded paired symbols. The second is to change theorder of arrangement of the precoded symbols. The former approach isdescribed as the first exemplary embodiment, and the latter approach asthe second exemplary embodiment.

First Exemplary Embodiment

FIGS. 5 to 11 are diagrams illustrating a principle of a method formapping precoded symbol pairs to resource elements according to thefirst exemplary embodiment of the present invention.

In order to simplify the explanation, FIGS. 5 to 11 are depicted underthe assumption that the number of subcarriers in an OFDM symbol of aresource block assigned, by a transmitter, to a receiver is n, which issimilar to the description with reference to FIGS. 3 and 4. Thesubcarriers are indexed from bottom to top of the resource block inorder of 0 to n−1. Meanwhile, the OFDM symbols are indexed from left toright in order of m and m+1.

The symbol mapping method according to the first exemplary embodimentcan include three schemes: 1) muting some subcarriers so as to not carrydata symbols, 2) transmitting symbols that are not SFBC-precoded on somesubcarriers, and 3) precoding between adjacent OFDM symbols on somesubcarriers.

First, a description is made of an exemplary method of muting somesubcarriers so as to not carry data symbols.

In case of SFBC, if the channels experienced by the paired symbols arespaced far apart, a demodulation error is likely to occur. In that case,the erroneously-demodulated symbol causes performance degradation inturbo code decoding. Accordingly, exemplary embodiments of the presentinvention propose a method for muting transmission of data symbols at aspecific position to avoid errors caused by paired symbols that arefar-apart.

Referring to parts (a) and (b) of FIG. 5, when the number of antennaports is equal to or less than 2 and the number of assigned resourceblocks is an odd number, the transmitter may not map any data symbol toone resource element in every OFDM symbol carrying the DM-RS in theassigned resource blocks. As shown in FIG. 5, no data symbol is mappedto the resource elements (m, 0) and (m+1, 0) of part (a) and theresource elements (m, n−2) and (m+1, 0) of part (b). By configuring suchthat a number of subcarriers carrying the SFBC-precoded data symbols inthe range of an assigned resource block becomes an even number in theaforementioned manner, the demodulation error caused by the pairedsymbols that are far-apart can be avoided.

Here, the position at which the corresponding subcarrier is to be mutedcan be placed at any of the empty resource elements that are notcarrying the reference signals, PBCH, or synchronization signals, in therange of the assigned resource block, in every OFDM symbol carrying theDM-RSs rather than fixed as in parts (a) and (b) of FIG. 5. Differentsubcarriers can be selected to be muted in the OFDM symbols having theDM-RSs.

Referring to part (a) of FIG. 6, when the number of antenna ports isequal to or less than 2, the transmitter can mute a subcarrier with thelowest index in every OFDM symbol carrying the DM-RS per resource blockregardless of the number of assigned resource blocks. In part (a) ofFIG. 6, the resource elements (m, 0) and (m+1, 0) are muted such thatdata symbols are not transmitted in these resource elements.

Referring to FIGS. 7 and 8, when the number of antenna ports is equal toor greater than 3, the transmitter can mute the same subcarrier acrossthe two OFDM symbols between the two pairs of code-division multiplexedreference groups regardless of the number of assigned resource blocks soas to prevent the demodulation error and remove the cause of thedecoding performance degradation problem.

As show in FIG. 7, the muting can be placed on the same subcarrier intwo contiguous OFDM symbols carrying the DM-RS. For example, in part (a)of FIG. 7, the resource elements (m, 4) and (m+1, 4) are positioned onthe same subcarrier.

As shown in FIG. 8, the muting can be placed on different subcarriers intwo contiguous OFDM symbols. For example, in part (a) of FIG. 8, theresource elements (m, 4) and (m+1, 2) are positioned on differentsubcarriers. Also, the muting can be placed on the same subcarrier inthe same resource block and on different subcarriers in a differentresource block. For example, in part (c) of FIG. 8, the resourceelements (m, 2) and (m+1, 2) are placed at the same positions in aresource block (RB 0) and, also in part (c) of FIG. 8, the resourceelements (m, n−5) and (m+1, n−3) are placed at different positions inthe different resource block (RB N−1).

However, the position of the subcarrier on which the muting is placed isnot limited to the cases as shown in FIGS. 7 and 8. That is, the methodincludes all the combinations fulfilling the conditions that only onesubcarrier, except for the two contiguous subcarriers between the twopairs of code-division multiplexed DM-RSs groups, is muted.

In all the aforementioned methods, the muted subcarrier can carry any ofChannel State Information Reference Signal (CSI-RS) and other controlsignal (except for the data symbol) or not.

At least one of the subcarrier muting methods can be supported by theLTE-A system. In case that two or more methods are supported, it isrequired to notify the receiver of the method to be used using aphysical layer control signal or an upper layer control signal. With thenotification about the muting method to be used, the receiver knows themuted positions and the positions on which other signals are transmittedas well as the precoded symbol positions.

At this time, if a signal other then the precoded symbol is transmittedat the corresponding position, the receiver performs demodulation on theresource elements only at the corresponding position with the methodappropriate for the corresponding signal and on resource elementscarrying precoded data symbols separately. In case that nothing istransmitted, the corresponding position is set to 0 so as to bedemodulated along with the precoded data symbols or excluded when theprecoded data symbols is demodulated.

Second, a description is made of an exemplary method for transmittingsymbols that are not SFBC-precoded on some subcarriers.

In SFBC, the precoded paired symbols that are spaced far apart causesdemodulation error. Moreover, the erroneously demodulated symbols resultin performance degradation for turbo code decoding. In order to preventthe demodulation error, exemplary embodiments of the present inventionpropose a method for transmitting data symbols that are notSFBC-precoded at specific positions.

Referring to parts (c) and (d) of FIG. 5, when the number of antennaports is equal to or less than 2 and an odd number of resource blocks isassigned, the transmitter can transmit a non-precoded data symbol on oneresource element in every OFDM symbol carrying the DM-RS. That is, theresource elements (m, 0) and (m+1, 0) in part (c) of FIG. 5 and theresource elements (m, n−2) and (m+1, 0) in part (d) of FIG. 5 can beused to transmit the non-precoded data symbols. By configuring such thata number of subcarriers carrying the SFBC-precoded data symbols in therange of an assigned resource block becomes an even number in theaforementioned manner, the demodulation error caused by the pairedsymbols that are far-apart can be avoided.

Here, the position at which the corresponding subcarriers is to be usedto carry the non-precoded symbol can be placed at any of the emptyresource elements that are not carrying the reference signals, PBCH, orsynchronization signals, in the range of the assigned resource block, inevery OFDM symbol carrying the DM-RSs rather than fixed as in parts (c)and (d) of FIG. 5. Different subcarriers can be selected to carry thenon-precoded data symbols in the OFDM symbols having the DM-RSs.

The following description illustrates a situation when the number ofantenna ports is equal to or less than 2 and the number of assignedresource blocks is not important.

Referring to part (b) of FIG. 6, when the number of antenna ports isequal to or less than 2, the transmitter can transmit thenon-SFBC-precoded data symbol on one subcarrier having the lowest index,per resource block, in every OFDM symbol having the DM-RSs. That is, theresource elements (m, 0) and (m+1, 0) in part (b) of FIG. 6 can be usedto carry the non-SFBC-precoded data symbols. In this manner, it ispossible to avoid the demodulation error and decoding performancedegradation.

The following description illustrates a situation when the number ofantenna ports is equal to or greater than 3 and the number of assignedresource blocks is not important.

Referring to FIGS. 9 and 10, when the number of antenna ports is equalto or greater than 3, the transmitter can transmit the non-SFBC precodeddata symbols on the subcarrier in two contiguous OFDM symbols having theDM-RSs between two pairs of code division multiplexed DM-RS groups inthe range of the assigned resource block. In this manner, it is possibleto improve the decoding performance.

The positions of the resource elements carrying the non-SFBC-precodeddata symbols can be placed on the same subcarrier in two contiguous OFDMsymbols having the DM-RSs as shown in FIG. 9. For example, the resourceelements (m, 4) and (m+1, 4) in part (a) of FIG. 9 illustrate such acase.

Referring to FIG. 10, the subcarrier index of the resource elementcarrying the non-precoded data symbol can be changed in the OFDM symbolsas the resource elements (m, 4) and (m+1, 2) illustrate in part (a) ofFIG. 10. Furthermore, the subcarrier index of the resource elementcarrying the non-precoded data symbol may not be changed as the resourceelements (m, 2) and (m+1, 2) in resource block (RB 0) of part (c)illustrate, or may be changed as the resource elements (m, n−5) and(m+1, n−3) in the resource block (RB N−1) of part (c) illustrate.

However, the positions of the subcarriers for carrying the non-precodeddata symbols are not limited to the configurations as depicted in FIGS.9 and 10. That is, the exemplary method includes all the combinationsfulfilling the conditions that only one subcarrier, except for the twocontiguous subcarriers between the two pairs of code-divisionmultiplexed DM-RSs groups, is used to carry the non-SFBC-precoded datasymbol.

At least one of the aforementioned exemplary methods for transmittingthe non-SFBC-precoded data symbols can be supported in the LTE-A system.In the case that two or more methods are used, the method to be appliedis notified to the receiver by means of a physical layer control signalor an upper layer control signal. With the notification about the methodto be used, the receiver knows the positions of the non-SFBC-precodeddata symbols so as to perform SFBC decoding on the remainingSFBC-precoded symbols.

Third, a description is made of an exemplary method of precoding acrossOFDM symbols on some subcarriers.

In case of SFBC, if the channels experienced by the paired symbols arespaced far apart, a demodulation error is likely to occur and, theerroneously-demodulated symbol causes performance degradation in turbocode decoding. Accordingly, exemplary embodiments of the presentinvention propose a method for precoding data symbols in adjacent OFDMsymbols rather than in the same OFDM symbol.

The following description illustrates a situation when the number ofantenna ports is equal to or less than 2 and an odd number of resourceblocks are assigned.

Referring to part (e) of FIG. 5, when the number of antenna ports isequal to or less than 2 and an odd number of resource blocks isassigned, the transmitter can perform precoding of the data symbols intothe resource elements of the adjacent OFDM symbols having the DM-RSrather than into the resource elements of the same OFDM symbol. Forexample, the transmitter may perform precoding of the data symbols intothe resource elements (m, 0) and (m+1, 0) of two adjacent OFDM symbolsas shown in part (e) of FIG. 5 so as to be paired. By configuring suchthat a number of subcarriers carrying the SFBC-precoded data symbols inthe range of an assigned resource block becomes an even number in theaforementioned manner, the demodulation error caused by the pairedsymbols that are far-apart can be avoided.

The following description illustrates a situation when the number ofantenna ports is equal to or less than 2 and the number of assignedresource blocks is not important.

Referring to part (c) of FIG. 6, when the number of antenna ports isequal to or less than 2, regardless of the number of assigned resourceblocks, the eNB can perform precoding on the data symbols into theresource elements of two different OFDM symbols, rather than the sameOFDM symbol, having the DM-RSs on the subcarrier having the lowest indexin the range of the assigned resource block. That is, the transmitterperforms precoding of the data symbols into the resource elements (m, 0)and (m+1, 0) and the resource elements (m, n−12) and (m+1, n−12) of twoadjacent OFDM symbols so as to be paired, respectively. In this manner,the demodulation error and decoding performance degradation problem canbe addressed

The following description illustrates a situation when the number ofantenna ports is equal to or greater than 3 and the number of assignedresource blocks is not important.

Referring to FIG. 11, when the number or antennas is equal to or greaterthan 3, regardless of the number of assigned resource blocks, thetransmitter can perform precoding on the data symbols into the resourceelements of two different OFDM symbols, rather than the same OFDMsymbol, having the DM-RSs on the same subcarrier, between two pairs ofcode division multiplexed DM-RS groups, in the range of the assignedresource block. In this manner, the decoding performance can beimproved. For example, the data symbols are precoded into the resourceelements (m, 4) and (m+1, 4) so as to be paired as shown in parts (a)and (b) of FIG. 11.

Here, the positions into which the data symbols are precoded in twoadjacent OFDM symbols are not limited to those depicted in FIG. 11. Thatis, the exemplary method includes all the combinations fulfilling theconditions that, except for the two contiguous subcarriers between thetwo pairs of code-division multiplexed DM-RSs groups, the data symbolsare precoded into the resource elements of the two contiguous OFDMsymbols on the same subcarriers.

At least one of the aforementioned methods for precoding across OFDMsymbols on some subcarriers can be supported in the LTE-A system. Incase that more than one precoding method is supported, the precodingmethod to be applied is notified to the receiver by means of a physicallayer control signal or an upper layer control signal. With thenotification about the precoding method to be used, the receiver knowswhere the SFBC precoding has been applied across two adjacent OFDMsymbols rather than in the same OFDM symbol. Accordingly, the receivercan decode the precoded symbols correctly into the data symbols.

Second Exemplary Embodiment

FIGS. 12 and 13 are diagrams illustrating arrangements of precodedsymbols mapped to REs in RBs according to a second exemplary embodimentof the present invention.

In order to simplify the explanation, FIGS. 12 and 13 are depicted underthe assumption that the number of subcarriers of a single OFDM symbol ofan RB assigned, by the transmitter, to the receiver is n and one RE iscomposed of 14 OFDM symbols. The subcarriers are indexed from bottom tothe top of the resource block in order of 0 to n−1. Meanwhile, the OFDMsymbols are indexed from left to right in order of 0 to 13. That is, thesubcarriers and the OFDM symbols are indexed in ascending order from 0.

Among the two aforementioned problems, the first problem is likely to bemore significant in view of the performance degradation per resourceelement. In order to address the first problem, exemplary embodiments ofthe present invention propose a resource mapping method different fromthe resource mapping method used in the convention LTE system.

The new resource mapping method for the LTE-A system is performed underfollowing conditions.

First, the PDSCH data symbols are not mapped to the positions carryingPBCH, synchronization signals, and reference signals.

Second, the PDSCH data symbols are not mapped in the OFDM symbolscarrying PDCCH.

The resources are assigned under these conditions.

Part (a) of FIG. 12 shows the arrangement of resource elements in aconventional LTE system and parts (b) and (c) of FIG. 12 show thearrangements of resource elements according to an exemplary embodimentof the present invention. As shown in FIG. 12, the resource mappingmethod according to an exemplary embodiment of the present inventionassigns the resource in an alternating or zigzag manner, i.e., inascending order of the subcarrier index in one OFDM symbol and then indescending order of the subcarrier index in next OFDM symbol. The dottedarrows show the direction of the resource assignment.

Referring to parts (b) and (c) of FIG. 12, resource assignment startsfrom the first subcarrier having the lowest index in the first OFDMsymbol following the control region (0, 3). If the resource assignmenthas been completed to the subcarrier having the highest index in theOFDM symbol (n−1, 3), the resource assignment restarts from thesubcarrier having the highest index in the next OFDM symbol (n−1, 4) tothe subcarrier having the lowest index (0, 4). If the resourceassignment has been completed to the subcarrier having the lowest indexin the OFDM symbol, the resource assignment restarts from the subcarrierhaving the lowest index in the next OFDM symbol (0, 5) to the lastsubcarrier and this is repeated until reaching last OFDM symbol of theresource block.

Although the resource assignment starts in ascending order first inparts (a) and (b) of FIG. 12, the present invention is not limitedthereto, i.e., the resource assignment can also start in descendingorder.

Referring to FIG. 13, the resource assignment direction is not changedfor the OFDM symbols having no DM-RS. As indicated by the dotted arrowsin FIG. 13, the resource assignment direction is changed for the OFDMsymbols having the DM-RS.

As shown in part (a) of FIG. 13, in OFDM symbols having no DM-RSs, theprecoded symbols are assigned a resource from the RE (0, 3) to the RE(n−1, 3) and then from the RE (0, 4) to the RE (N−1, 4) in ascendingorder. Next, in the OFDM symbols having DM-RSs, the precoded symbols areassigned a resource from the RE (0, 5) to the RE (n−1, 5) in ascendingorder and then from the RE (n−1, 6) to the RE (0, 6) in descendingorder.

Also, exemplary embodiments of the present invention include the methodfulfilling the conditions that the resource assignment is performed inan identical direction in the OFDM symbols having no DM-RS in anyconfiguration different from that shown in FIG. 13, but in oppositedirections in the two contiguous OFDM symbols having DM-RSs.

In the LTE-A system, the resource mapping can be performed only with anew resource assignment method or with a new resource assignment methodand a conventional resource assignment method selectively depending onthe implementation. In case that both a new resource assignment methodand a selective resource assignment method are implemented, the resourceassignment method used by the transmitter is notified to the receiver bymeans of a physical layer signal or an upper layer control signal. Withthis notification, the receiver can recognize the positions where thedata symbols are mapped so as to perform the demodulation correctlyusing the conventional SFBC demodulation method.

Among the methods described in the first and second exemplaryembodiments, only one method can be fixedly used or more than one methodcan be used selectively depending on the case. Also, it is possible touse more than two methods simultaneously. In some cases, one or moremethods can be used fixedly. In this case, the transmitter can notifythe receiver of the method applied by means of a physical layer controlsignal or an upper layer control signal. Accordingly, the receiver canperform a reception operation with the notified method.

FIG. 14 is a block diagram illustrating a configuration of a transmitteraccording to an exemplary embodiment of the present invention.

Referring to FIG. 14, the transmitter 100 includes a scrambler 110, amodulator 120, a layer mapper 130, a precoder 140, a resource elementmapper 150, and an OFDM symbol generator 160.

In case of using multiple antennas, the transmission data aretransmitted with one or more codewords. In case of using multiplecodewords according to an exemplary embodiment of the present invention,when the data as codewords are input, the scrambler 110 performsscrambling on the input data.

The modulator 120 performs modulation on the scrambled data. Themodulation can be performed with one of QPSK, 4QAM, and 16QAM.

The layer mapper 130 maps the modulation data input in series to thecorresponding layers. More particularly, the layer mapper 130 includes aprecoding pair selector 131.

The precoding pair selector 131 selects a pair of symbols to be precodedand outputs the paired symbols to the precoder 140. More particularly,the precoding pair selector 131 can output a pair of symbols that aretransmitted on some subcarriers without being precoded according to thefirst exemplary embodiment of the present invention. This method hasbeen described above with reference to parts (c) and (d) of FIG. 5, andpart (b) of FIG. 6, FIG. 9, and FIG. 10.

The precoding pair selector 131 also can select and output a pair ofsymbols to be precoded in the adjacent OFDM symbols on some subcarriersaccording to the first exemplary embodiment of the present invention.This method has been described above with reference to part (e) of FIG.5, part (c) of FIG. 6 and FIG. 11.

The precoder 140 performs precoding in units of a pair of symbols andoutputs the precoded paired symbols in units of symbol in series.

The resource element mapper 150 is responsible for mapping the precodedsymbols in the downlink frame per UE. That is, the resource elementmapper 150 is responsible for mapping the precoded paired symbols toresource elements.

More particularly, the resource element mapper 150 can map the symbolssuch that the precoded symbols are not arranged on specific subcarriersaccording to the first exemplary embodiment of the present invention.This method has been described with reference to parts (a) and (b) ofFIG. 5, and part (c) of FIG. 7 and FIG. 8.

The resource element mapper 150 can map the symbols such that theprecoded paired symbols are arranged at different position in differentOFDM symbols.

The OFDM symbol generator 160 performs modulation on the mapped (orarranged) precoded symbols into OFDM signals so as to be transmittedthrough antennas.

FIG. 15 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment of the present invention.

Referring to FIG. 15, the receiver 200 includes an OFDM demodulator 210,a resource element demapper 220, a Log-Likelihood Ratio (LLR) generator230, a channel decoder 240, an information data extractor 250, areference signal extractor 260, and a channel estimator 270.

As described above, the transmitter 100 notifies the receiver 200 of oneor a combination of resource mapping methods that has been used for theresource arrangement. At this time, the transmitter 100 can notify thereceiver 200 of the resource mapping method by means of a physical layercontrol signal or an upper layer control signal. It is assumed, in thefollowing description, that the receiver 200 knows the resource mappingmethod used by the transmitter through this notification.

The OFDM demodulator 210 performs demodulation on the received OFDMsignal and outputs the demodulated OFDM signal.

The reference signal extractor 260 extracts reference signals in unitsof OFDM symbols, and the channel estimator 270 estimates a channel basedon the resource signals.

The resource element demapper 220 extracts the precoded symbols from theresource elements according to the resource mapping method transmittedby the transmitter 100.

More particularly when the transmitter 100 has not mapped any precodedpaired symbols on specific subcarriers according to the first exemplaryembodiment of the present invention, the resource element demapper 220skips the extraction operation on the corresponding resource elements.This method has been described with reference to parts (a) and (b) ofFIG. 5, and part (a) of FIG. 6, FIG. 7, and FIG. 8.

Also, when the transmitter 100 has mapped the precoded paired symbols toresource elements on different subcarriers in different OFDM symbolsaccording to the second exemplary embodiment of the present invention,the resource element demapper 220 extracts the symbols from thecorresponding resource elements as mapped by the transmitter. Thismethod has been described with reference to FIGS. 12 and 13.

The LLR generator 230 computes the LLR value with the channel estimationvalue and outputs the computed LLR value. More particularly, the LLRgenerator 230 includes a symbol decoder 231. The symbol decoder 231performs decoding on the precoded symbols according to the SFBC scheme.More particularly when the transmitter 100 has not mapped non-precodedsymbols on some subcarriers according to the first exemplary embodimentof the present invention, the symbol decoder 231 determines thepositions of the resource elements to which the non-precoded symbols aremapped and then skips decoding on the corresponding resource elements.As described above, the non-precoded symbol position acquisition methodcan be notified to the receiver 200 through an upper layer signaling.This method has been described with reference to parts (c) and (d), ofFIG. 6, and part (b) of FIGS. 9 and 10.

Also, when the transmitter 100 has transmitted the paired symbols intotwo adjacent OFDM symbols according to the first exemplary embodiment ofthe present invention, the symbol decoder 231 determines the positionsof the resource elements to which the precoded paired symbols in the twoadjacent OFDM symbols and performs SFBC decoding on the correspondingresource elements along with the resource elements carrying the normallymapped symbols. As described above, the symbol position acquisitionmethod can be notified to the receiver 200 through an upper layersignaling. This method has been described with reference to part (e) ofFIG. 5, part (c) of FIG. 6, and FIG. 11.

If a pair of decoded symbols are input, the channel decoder 240 performsdecoding on the data based on the LLR. The data decoding can be done bya turbo code decoding scheme.

The information data extractor 250 extracts original information datafrom the value decoded by the channel decoder 240. The information datacan be extracted in units of codeword.

Hereinafter, a description is made under the assumption that thetransmitter and receiver share the resource mapping method according toan exemplary embodiment of the present invention with reference to FIGS.16 and 17. In the resource mapping method, the transmitter 100 notifiesthe receiver 200 of the applied resource mapping method through an upperlayer signaling.

FIG. 16 is a flowchart illustrating a resource element mapping method ofa transmitter according to an exemplary embodiment of the presentinvention.

Referring to FIG. 16, the transmitter performs modulation on the data tobe transmitted in step 1610. Here, the modulation is performed with oneof a plurality of modulation schemes including QPSK, 4QAM, and 16QAM.

Next, the transmitter maps the modulated data to corresponding layersand selects a pair of symbols to be precoded in unit of symbol in step1603. At this time, the transmitter can select a pair of symbols thatare not precoded and transmitted on some subcarriers according to thefirst exemplary embodiment of the present invention. This method hasbeen described with reference to parts (c) and (d) of FIG. 5, part (b)of FIG. 6, and FIGS. 9 and 10. The transmitter also can output a pair ofsymbols that can be precoded into the resource elements in two adjacentOFDM symbols on some subcarriers according to the first exemplaryembodiment of the present invention. This method has been described withreference to part (e) of FIG. 5, part (c) of FIG. 6, and FIG. 11.

Next, the transmitter performs precoding on the selected symbols in step1605.

Next, the transmitter maps the precoded paired symbols to the resourceelements in step 1607. At this time, the transmitter may vacate theresource elements on specific subcarriers rather than mapping theprecoded paired symbols according to the first exemplary embodiment ofthe present invention. This method has been described with reference toparts (a) and (b) of FIG. 5, part (a) of FIG. 6, and FIGS. 7 and 8. Thetransmitter also can map the precoded paired symbols to the resourceelements on different subcarriers in different OFDM symbols according tothe second exemplary embodiment of the present invention. This methodhas been described with reference to FIGS. 12 and 13.

Next, the transmitter performs OFDM modulation on the mapped symbols onthe time axis in step 1609 and transmits the OFDM modulated signal instep 1611.

FIG. 17 is a flowchart illustrating a resource element demapping methodof a receiver according to an exemplary embodiment of the presentinvention.

Referring to FIG. 17, the receiver receives signals in step 1701 andperforms OFDM demodulation on the received signal in step 1703.

The receiver extracts reference signals from the demodulated signal andestimates a channel based on the extracted reference signals. Thereceiver also compensates for the value when demodulating the data onthe estimated channel. Since the compensation method is out of the scopeof the present invention, a detailed description is omitted herein.

Next, the receiver performs demapping on the OFDM demodulated signal atcorresponding resource elements in step 1705. When the transmitter hasnot mapped the precoded symbols to the resource elements on specificsubcarriers according to the first exemplary embodiment of the presentinvention, the receiver skips extracting symbols on the correspondingresource elements. This method has been described with reference toparts (a) and (b) of FIG. 5, part (a) of FIG. 6, and FIGS. 7 and 8.Also, when the transmitter has mapped the precoded paired symbols to theresource elements on different subcarriers in different OFDM symbolsaccording to the second exemplary embodiment of the present invention,the receiver extracts these symbols at corresponding resource elementsas mapped by the transmitter. This method has been described withreference to FIGS. 12 and 13.

Next, the receiver performs SFBC decoding in step 1707. At this time,when the transmitter has mapped the non-precoded symbols to the resourceelements on some subcarriers according to the first exemplary embodimentof the present invention, the receiver determines the positions of theresource elements to which the non-precoded symbols are mapped and skipsdecoding at the corresponding resource elements. As described above, thetransmitter can notify the receiver of the non-precoded symbols positionacquisition method through an upper layer signaling. This method hasbeen described with reference to parts (c) and (d) of FIG. 5, part (b)of FIG. 6, and FIGS. 9 and 10. Also, when the transmitter has mapped theprecoded symbols to the resource elements on different subcarriers intwo adjacent OFDM symbols, the receiver determines the positions of theresource elements to which the precoded symbols are mapped in theadjacent OFDM symbols and performs SFBC decoding on the correspondingpaired symbols. As aforementioned, the transmitter can notify thereceiver of the precoded symbol position acquisition method through anupper layer signaling. This method has been described with reference topart (b) of FIG. 5, part (c) of FIG. 6, and FIG. 11.

Next, the receiver performs channel decoding in step 1709. The receivercalculates the LLR value from the symbol data and performs channeldecoding based on the calculated LLR value. Next, the receiver extractsthe original information data from the channel-decoded values in step1711.

A description is made of an exemplary method for mapping the channelstate information reference signal hereinafter with reference to FIGS.18 to 32.

FIG. 18 is a diagram illustrating arrangements of channel stateinformation reference signals in resource blocks used in an LTE systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 18, the Channel State Information Reference Signal(CSI-RS) is the reference signal transmitted for the UE to measure thechannel state. The CSI-RS is transmitted from the eNB to the UEs. Unlikethe Common Reference Signal (CRS) of an LTE system which is transmittedin every subframe, the CSI-RS is transmitted at a regular interval. TheCSI-RSs are mapped in resource blocks as shown in FIG. 18.

In an LTE system, the precoded symbols are mapped to the resourceelements according to the following procedure. The LTE system uses theSFBC for achieving transmission diversity, such that the number ofprecoded symbols to be mapped to the resource elements must be multipleof 2. Under the basic assumption for applying the SFBC, the precodedpaired symbols must experience the same or similar channel environment.It is preferred that the precoded paired symbols are mapped to resourceelements positioned closely to each other. The CRSs of the LTE system ofFIG. 1 shows a representative example of the reference signalarrangement.

FIG. 19 is a diagram illustrating a principle of the precoded pairedsymbol mapping in an LTE system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 19, a case is illustrated in which the precoded pairedsymbols are arranged in an OFDM symbol having the CRSs of four antennaports. Each pair of precoded symbols is connected through a solid line.Accordingly, it can be observed that a pair of symbols that areSFBC-precoded are mapped to resource elements on the adjacentsubcarriers.

Although the CRS of LTE is partially used, the LTE-A system adopts theCSI-RS as shown in FIG. 18 for measuring channel state. With theintroduction of the CSI-RS, it is likely to degrade the systemperformance to apply the transmission diversity and resource mappingscheme used in the LTE system to the LTE-A system without modification.

In other words, the number of resource elements to which the precodedsymbols can be mapped in an OFDM symbol carrying the CSI-RS can be anodd number or not be a multiple of 4 as shown in FIG. 18. In this case,the SFBC-precoded paired symbols can be mapped to the REs that arespaced far apart from each other when using the conventional resourceassignment rule so as to experience different channel environments,resulting in performance degradation.

In the LTE-A system, the CRSs for 1, 2, and 4 antenna ports and theCSI-RSs for 1, 2, 4, and 8 antenna ports can be freely arranged.Accordingly, when the CRSs of two antenna ports are transmitted, theCRSs can be arranged along with the CSI-RSs of one or two antenna ports.

FIG. 20 is a diagram illustrating exemplary arrangements of precodedpaired symbols when the number of CRS antenna ports is 2 and the numberof CSI-RS antenna ports is 1 in the LTE-A system according to anexemplary embodiment of the present invention. That is, FIG. 20 showsthe arrangements of the CRSs of two antenna ports and the CSI-RSs of oneantenna port.

Referring to FIG. 20, the symbols positioned at the top and bottom ofthe RBs, colored distinctly, and linked by a solid line are the pairedsymbols causing the performance degradation. The performance-degradingpaired symbols can be determined depending when the number of assignedRBs is odd number or even number as shown in parts (a) and (b) of FIG.20.

FIG. 21 is a diagram illustrating exemplary arrangements of the precodedpaired symbols when the number of CRS antenna ports is 2 and the numberof CSI-RS antenna ports is 2 in the LTE-A system according to anexemplary embodiment of the present invention. FIG. 22 is a diagramillustrating exemplary arrangements of the precoded paired symbols whenthe number of CRS antenna ports is 4 and the number of CSI-RS antennaports is 1 in the LTE-A system according to an exemplary embodiment ofthe present invention. FIG. 23 is a diagram illustrating exemplaryarrangements of the precoded paired symbols when the number of CRSantenna ports is 4 and the number of CSI-RS antenna ports is 2 in theLTE-A system according to an exemplary embodiment of the presentinvention. In FIGS. 21 to 23, the symbols linked by solid lines andillustrated with different shading are the performance-degrading pairedsymbols.

The performance degradation of the transmission diversity in the LTE-Asystem is caused by SFBC-precoded paired symbols that are not mapped toadjacent REs. Resource mapping methods that are capable of overcomingthe transmission diversity performance degradation problem in the LTE-Asystem are proposed in the third and fourth exemplary embodiments of thepresent invention.

Third Exemplary Embodiment

In order to overcome the transmission diversity performance degradationproblem, an exemplary method for mapping the precoded symbols tospecific resource elements is proposed. An exemplary precoded symbolmapping method is described with reference to FIGS. 24 to 27.

FIG. 24 is a diagram illustrating an arrangement of the precoded pairedsymbols when the number of CRS antenna ports is 2 and the number ofCSI-RS antenna ports is 1 in the LTE-A system according to an exemplaryembodiment of the present invention. FIG. 25 is a diagram illustratingarrangements of the precoded paired symbols when the number of CRSantenna ports is 2 and the number of CSI-RS antenna ports is 2 in theLTE-A system according to an exemplary embodiment of the presentinvention. FIG. 26 is a diagram illustrating arrangements of theprecoded paired symbols when the number of CRS antenna ports is 4 andthe number of CSI-RS antenna ports is 1 in the LTE-A system according toan exemplary embodiment of the present invention. FIG. 27 is a diagramillustrating arrangements of the precoded paired symbols when the numberof CRS antenna ports is 4 and the number of CSI-RS antenna ports is 2 inthe LTE-A system according to an exemplary embodiment of the presentinvention.

The following description illustrates a situation having a CRS of twoantenna ports and a CSI-RS of one antenna port.

Referring to FIG. 24, the RB is configured such that the number of REsto be used for PDCCH transmission in an OFDM symbol becomes an evennumber to avoid that the SFBC-precoded paired symbols are mapped to theREs spaced far apart from each other. In this case, the SFBC can be usedfor transmission diversity, and one of the REs adjacent to the CSI-RS inthe OFDM symbol having the CSI-RS is maintained in an empty state asshown in FIG. 24. To maintain an RE in an empty state means that nothingis mapped to the corresponding RE. The RE to be transmitted in an emptystate is determined according to the following rule: The REs belongingto an OFDM symbol in an RB are indexed in ascending order with which theresource is assigned in the LTE system. That is, the first RE of theOFDM symbol in the RB is assigned the index 0 and the last RE isassigned the index 11.

In case that the index n of the RE to which a CSI-RS is mapped is an oddnumber (mod(n, 2)=1), the RE having an index n−1 in the OFDM carryingthe CSI-RS is transmitted in an empty state. In case that the index n ofthe RE to which a CSI-RS is mapped in an even number (mod(n, 2)=0), theRE having an index n+1 in the OFDM carrying the CSI-RS is transmitted inan empty state.

The following description illustrates a situation having a CRS of twoantenna ports and a CSI-RS of two antenna ports.

Referring to FIG. 25, the SFBC can be applied for transmission diversityin which case the REs adjacent to the REs to which one CSI-RS is mappedare transmitted in an empty state in the OFDM symbols carrying theCSI-RS. As illustrated, when the CSI-RSs of the two antenna ports aretransmitted, the CSI-RSs are mapped to the REs on the same subcarrier intwo contiguous OFDM symbols. Here, the REs to be transmitted in an emptystate are the ones positioned adjacent to the REs to which the CSI-RSsare mapped in the OFDM symbols carrying the CSI-RSs. The REs to betransmitted in an empty state are determined according to the followingrule: In case that the index n of the RE to which a CSI-RS is mapped isan odd number (mod(n, 2)=1), the RE having an index n−1 in the OFDMsymbol carrying the CSI-RS is transmitted in an empty state. In casethat the index n of the RE to which a CSI-RS is mapped in an even number(mod(n, 2)=0), the RE having an index n+1 in the OFDM carrying theCSI-RS is transmitted in an empty state.

The following description illustrates a situation having a CRS of fourantenna ports and CSI-RS of one antenna port.

Referring to FIG. 26, the FSTD can be applied for transmission diversityin which case three REs can be transmitted in an empty state in an OFDMsymbol carrying the CSI-RS. The CSI-RSs, as shown in FIG. 18, are mappedto the four or twelve REs in one OFDM symbol within an RB. In case thatthe CSI-RSs can be mapped to four REs, the three REs, excluding the REmapped to the CSI-RS, can be transmitted in an empty state as shown inpart (a) of FIG. 26. In the case that CSI-RSs can be mapped to twelveREs, the three REs adjacent to the REs to which the current CSI-RSs aremapped can be transmitted in an empty state as shown in part (b) of FIG.26. Here, the REs to be transmitted in an empty state are determinedaccording to the following rule:

If └n÷4┘=0 is applied to the index n of the RE to which a CSI-RS ismapped, the three REs fulfilling └n÷4┘=0, excluding the RE to which thecurrent CSI-RS is mapped, in the OFDM symbol carrying the CSI-RS aretransmitted in an empty state. If └n÷4┘=1 is applied to the index n ofthe RE to which a CSI-RS is mapped, the three REs fulfilling └n÷4┘=1,excluding the RE to which the current CSI-RS is mapped, in the OFDMsymbol carrying the CSI-RS are transmitted in an empty state. If └n÷4┘=2is applied to the index n of the RE to which a CSI-RS is mapped, thethree REs fulfilling └n÷4┘=2, excluding the RE to which the currentCSI-RS is mapped, in the OFDM symbol carrying the CSI-RS are transmittedin an empty state. Finally, if └n÷4┘=3 is applied to the index n of theRE to which a CSI-RS is mapped, the three REs fulfilling └n÷4┘=3,excluding the RE to which the current CSI-RS is mapped, in the OFDMsymbol carrying the CSI-RS are transmitted in an empty state.

The following description illustrates a situation having a CRS of fourantenna ports and a CSI-RS of two antenna ports.

Referring to FIG. 27, the FSTD can be applied for transmission diversityin which case the REs adjacent to the RE to which the CSI-RS are mappedin the OFDM symbol carrying the CSI-RS can be transmitted in an emptystate. In case that there are the CSI-RSs of two antenna ports, theCSI-RSs are mapped to the REs on the same subcarrier in the two adjacentOFDM symbols as shown in FIG. 27. Accordingly, the RE adjacent to the REwhich is mapped to the CSI-RS in each OFDM symbol carrying the CSI-RS istransmitted in an empty state. The REs to be transmitted in an emptystate are determined according to the following rule: In case that theindex n of the RE to which a CSI-RS is mapped is an odd number (mod(n,2)=1), the RE having an index n−1 in the OFDM symbol carrying the CSI-RSis transmitted in an empty state. In case that the index n of the RE towhich a CSI-RS is mapped is an even number (mod(n, 2)=0), the RE havingan index n+1 in the OFDM carrying the CSI-RS is transmitted in an emptystate.

One or more of the aforementioned exemplary methods for transmitting theREs on some subcarriers in an empty state can be supported in the LTE-Asystem. In case that more than one method is supported, the eNB cannotify the UE of the applied method through a physical layer signalingor an upper layer signaling. Accordingly, the UE has the knowledge aboutpositions on the subcarriers where no signal is transmitted or controlsignals are transmitted.

The signals (e.g., control signals) other than precoded symbols aremapped to the REs, the UE performs modulation on the correspondingpositions in appropriate method. At this time, the UE demodulates thepositions at which the data symbols are precoded separately. The UE setthe value of the REs that have been transmitted in an empty state tonull (0) and performs demodulation on the precoded symbols and othersignals. Also, the UE can perform demodulation on the precoded symbolson the resource excluding specific positions.

Fourth Exemplary Embodiment

In an LTE-A system, a new resource mapping method is need in order toaddress the aforementioned problem occurring in the conventionalresource mapping method used in the LTE system in which the modulationsymbols are mapped to corresponding layers and then sequentiallySFBC-precoded in pairs. Exemplary embodiments of the present inventionpropose the following methods to address the aforementioned problems.

An exemplary method is to map non-SFBC precoded symbols to some REs.

In SFBC, if a pair of precoded symbols experience largely differentchannel environments, this is likely to cause demodulation error. Thedemodulation error causes performance degradation in a turbo codedecoding process. In order to avoid the demodulation error, exemplaryembodiments of the present invention propose a resource mapping methodin which non-SFBC precoded data symbols are mapped to specific REs.

In this resource mapping method, a pair of symbols that are not precodedin SFBC are mapped to the REs located at specific positions. The RE towhich the non-precoded symbol is mapped can be determined by a fewexemplary methods. These methods are described with reference to FIGS.28 to 31.

FIG. 28 is a diagram illustrating an arrangement of non-precoded symbolswhen the number of CRS antenna ports is 2 and the number of CSI-RSantenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention. FIG. 29 is a diagram illustratingan arrangement of non-precoded symbols when the number of CRS antennaports is 2 and the number of CSI-RS antenna ports is 2 in an LTE-Asystem according to an exemplary embodiment of the present invention.FIG. 30 is a diagram illustrating an arrangement of the non-precodedsymbols when the number of CRS antenna ports is 4 and the number ofCSI-RS antenna ports is 1 in an LTE-A system according to an exemplaryembodiment of the present invention. FIG. 31 is a diagram illustratingan arrangement of non-precoded symbols when the number of CRS antennaports is 4 and the number of CSI-RS antenna ports is 2 in an LTE-Asystem according to an exemplary embodiment of the present invention.

The following description illustrates a situation having a CRS of twoantenna ports and a CSI-RS of one antenna port.

Referring to FIG. 28, SFBC can be applied for transmission diversity,but the SFBC is not applied to one of the REs adjacent to the RE towhich the CSI-RS is mapped in the OFDM symbol carrying the CSI-RSaccording to an exemplary embodiment of the present invention.

The REs are indexed in an RB as follows: the REs belonging to an OFDMsymbol in an RB is indexed in ascending order with which the resource isassigned. In this case, the first RE of the OFDM symbol in the RB isassigned the index 0 and the last RE is assigned the index 11.

In case that the index n of the RE to which a CSI-RS is mapped is an oddnumber (mod(n, 2)=1), the RE having an index n−1 in the OFDM carryingthe CSI-RS is transmitted with non-SFBC-precoded symbol. In case thatthe index n of the RE to which a CSI-RS is mapped in an even number(mod(n, 2)=0), the RE having an index n+1 in the OFDM carrying theCSI-RS is transmitted with non-SFBC-precoded symbol.

The following description illustrates a situation having a CRS of twoantenna ports and a CSI-RS of two antenna ports.

Referring to FIG. 29, the SFBC can be applied for transmission diversityin which case the REs adjacent to the REs to which one CSI-RS is mappedare transmitted with non-SFBC-precoded symbol in the OFDM symbolscarrying the CSI-RS. As illustrated, when the CSI-RSs of the two antennaports are transmitted, the CSI-RSs are mapped to the REs on the samesubcarrier in two contiguous OFDM symbols. Here, the REs to betransmitted with non-SFBC-precoded symbol are the ones positionedadjacent to the REs to which the CSI-RSs are mapped in the OFDM symbolscarrying the CSI-RSs.

In case that the index n of the RE to which a CSI-RS is mapped is an oddnumber (mod(n, 2)=1), the RE having an index n−1 in the OFDM symbolcarrying the CSI-RS is transmitted with non-SFBC-precoded symbol. Incase that the index n of the RE to which a CSI-RS is mapped is an evennumber (mod(n, 2)=0), the RE having an index n+1 in the OFDM carryingthe CSI-RS is transmitted with non-SFBC-precoded symbol.

The following description illustrates a situation having a CRS of fourantenna ports and a CSI-RS of one antenna port.

Referring to FIG. 20, the FSTD can be applied for transmission diversityin which case three REs can be transmitted in an empty state in an OFDMsymbol carrying the CSI-RS. The CSI-RSs, as shown in FIG. 18, are mappedto the four or twelve REs in one OFDM symbol within an RB. In case thatthe CSI-RSs can be mapped to four REs, the three REs, excluding the REmapped to the CSI-RS, can be transmitted with non-SFBC-precoded symbolas shown in part (a) of FIG. 30. In case that CSI-RSs can be mapped totwelve REs, the three REs adjacent to the REs to which the currentCSI-RSs are mapped can be transmitted with non-SFBC-precoded symbol asshown in part (b) of FIG. 30. Here, the REs to be transmitted withnon-SFBC-precoded symbol are determined according to the following rule:If └n÷4┘=0 is applied to the index n of the RE to which a CSI-RS ismapped, the three REs fulfilling └n÷4┘=0, excluding the RE to which thecurrent CSI-RS is mapped, in the OFDM symbol carrying the CSI-RS aretransmitted with non-SFBC-precoded symbol. If └n÷4┘=1 is applied to theindex n of the RE to which a CSI-RS is mapped, the three REs fulfilling└n÷4┘=1, excluding the RE to which the current CSI-RS is mapped, in theOFDM symbol carrying the CSI-RS are transmitted with non-SFBC-precodedsymbol. If └n÷4┘=2 is applied to the index n of the RE to which a CSI-RSis mapped, the three REs fulfilling └n÷4┘=2, excluding the RE to whichthe current CSI-RS is mapped, in the OFDM symbol carrying the CSI-RS aretransmitted with non-SFBC-precoded symbol. Finally, if └n÷4┘=3 isapplied to the index n of the RE to which a CSI-RS is mapped, the threeREs fulfilling └n÷4┘=3, excluding the RE to which the current CSI-RS ismapped, in the OFDM symbol carrying the CSI-RS are transmitted withnon-SFBC-precoded symbol.

The following description illustrates a situation having a CRS of fourantenna ports and a CSI-RS of two antenna ports.

Referring to FIG. 31, the FSTD can be applied for transmission diversityin which case the REs adjacent to the RE to which the CSI-RS are mappedin the OFDM symbol carrying the CSI-RS can be transmitted withnon-SFBC-precoded symbol. In case that there are the CSI-RSs of twoantenna ports, the CSI-RSs are mapped to the REs on the same subcarrierin the two adjacent OFDM symbols as shown in FIG. 31. Accordingly, theRE adjacent to the RE which is mapped to the CSI-RS in each OFDM symbolcarrying the CSI-RS is transmitted with non-SFBC-precoded symbol, andthe REs to be transmitted with non-SFBC-precoded symbol are determinedaccording to the following rule: In case that the index n of the RE towhich a CSI-RS is mapped is an odd number (mod(n, 2)=1), the RE havingan index n−1 in the OFDM symbol carrying the CSI-RS is transmitted withnon-SFBC-precoded symbol. In case that the index n of the RE to which aCSI-RS is mapped is an even number (mod(n, 2)=0), the RE having an indexn+1 in the OFDM carrying the CSI-RS is transmitted withnon-SFBC-precoded symbol.

One or more of the aforementioned exemplary methods for transmitting theREs on some subcarriers with a non-SFBC-precoded symbol can be supportedin the LTE-A system. In case that more than one method is supported, theeNB can notify the UE of the applied method through a physical layersignaling or an upper layer signaling. Accordingly, the UE has theknowledge about positions on the subcarriers where the non-SFBC-precodedsymbol or control signals are transmitted. Based on this knowledge, theUE demodulates the symbols mapped to the corresponding REs without SFBCdecoding. The UE also performs SFBC decoding on the precoded symbolsmapped to the remaining REs, excluding the symbols mapped to thecorresponding REs.

The second exemplary method is to perform precoding across adjacentsymbols on some subcarriers.

FIG. 32 is a diagram illustrating an arrangement of inter-OFDM-precodedsymbols in an LTE-A system according to an exemplary embodiment of thepresent invention.

In SFBC, if a pair of precoded symbols experience largely differentchannel environments, this is likely to cause demodulation error. Thedemodulation error causes performance degradation in a turbo codedecoding process. In order to avoid the demodulation error, exemplaryembodiments of the present invention propose a resource mapping methodin which a pair of data symbols is precoded into the REs across twoadjacent OFDM symbols. The resource mapping method according to thefifth exemplary embodiment of the present invention can be applied toonly to the case where the CSI-RSs of two antenna ports are transmittedunlike the aforementioned other methods.

In this case, the REs adjacent to the REs to which the CSI-RSs aremapped are SFBC-precoded across the OFDM symbols having the CSI-RSregardless of the number of antenna ports of the CSI-RSs as shown inFIG. 32. In case that the CSI-RSs of two antenna ports are transmittedas shown in FIG. 32, the CSI-RSs are mapped to the REs on the samesubcarrier across two adjacent OFDM symbols. Accordingly, the REs to beprecoded across two OFDM symbols are the REs adjacent to the REs towhich the CSI-RSs are mapped in the OFDM symbols having the CSI-RS. TheREs to be precoded across two OFDM symbols are determined as follows: Incase that the index n of the RE to which a CSI-RS is mapped is an oddnumber (mod(n, 2)=1), the RE having an index n−1 in the OFDM carryingthe CSI-RS is transmitted with an inter-OFDM symbol-precoded symbol. Incase that the index n of the RE to which a CSI-RS is mapped is an evennumber (mod(n, 2)=0), the RE having an index n+1 in the OFDM carryingthe CSI-RS is transmitted with an inter-OFDM symbol-precoded symbol.

One or more of the aforementioned exemplary methods for transmitting theREs on some subcarriers with an inter-OFDM symbol-precoded symbol can besupported in the LTE-A system. In case that more than one method issupported, the eNB can notify the UE of the applied method through aphysical layer signaling or an upper layer signaling. Accordingly, theUE has the knowledge about positions on the subcarriers where theinter-OFDM symbol-precoded symbol or control signals are transmitted.Based on this knowledge, the UE demodulates the symbols mapped to thecorresponding REs with SFBC decoding.

Among the aforementioned exemplary methods, the LTE-A system can operatewith one fixed method, all of them selectively, or a combination of atleast two of them. Except for the case of using the fixed method, theeNB notifies the UE of the resource mapping method applied for thetransmission by means of a physical layer control signal or an upperlayer control signal. Accordingly, the user can receive the signals withan appropriate resource mapping method.

As described above, exemplary resource mapping methods of the presentinvention are capable of avoiding the decoding performance degradationand the demodulation error caused by paired symbols that are far-apart.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of transmitting data in a wirelesscommunication system using transmission diversity, the methodcomprising: precoding data symbols; determining whether a number ofresource elements available for transmitting the precoded data symbolsin an Orthogonal Frequency Division Multiplexing (OFDM) symbol in aresource block is odd; mapping the precoded data symbols to theavailable resource elements; and transmitting the precoded data symbolsmapped to the available resource elements, wherein, if the number ofresource elements available for transmitting the precoded data symbolsin the OFDM symbol of the resource block is odd, the precoded datasymbols are not mapped to at least one of the available resourceelements.
 2. The method of claim 1, wherein the OFDM symbol contains aChannel State Information Reference Signal (CSI-RS).
 3. The method ofclaim 1, wherein the precoding of data symbols comprises maintaining atleast one pair of data symbols non-precoded.
 4. The method of claim 1,wherein the precoding of data symbols comprises selecting a pair of datasymbols to be precoded on a subcarrier across at least one pair of OFDMsymbols.
 5. A method of transmitting data in a wireless communicationsystem using transmission diversity, the method comprising: precodingdata symbols; determining, from among resource elements in an OrthogonalFrequency Division Multiplexing (OFDM) symbol available for transmittingthe precoded data symbols, whether resource elements to be mapped fortransmitting the precoded data symbols are separated by two or moreindexes; mapping the precoded data symbols to the resource elements; andtransmitting the precoded data symbols mapped to the resource elements,wherein, if the resource elements to be mapped for transmitting theprecoded data symbols in the OFDM symbol are separated by two or moreindexes, the precoded data symbols are not mapped to at least one of theavailable resource elements.
 6. The method of claim 5, wherein the OFDMsymbol contains a Channel State Information Reference Signal (CSI-RS).7. The method of claim 5, wherein the precoding of data symbolscomprises maintaining at least one pair of data symbols non-precoded. 8.The method of claim 5, wherein the precoding of data symbols comprisesselecting a pair of data symbols to be precoded on a subcarrier acrossat least one pair of OFDM symbols.
 9. An apparatus for transmitting datain a wireless communication system using transmission diversity, theapparatus comprising: a precoder for precoding data symbols; adetermining unit for determining whether a number of resource elementsavailable for transmitting the precoded data symbols in an OrthogonalFrequency Division Multiplexing (OFDM) symbol in a resource block isodd; a resource element mapper for mapping the precoded data symbols tothe available resource elements; and a transceiver for transmitting theprecoded data symbols mapped to the available resource elements,wherein, if the number of resource elements available for transmittingthe precoded data symbols in the OFDM symbol of the resource block isodd, the precoded data symbols are not mapped to at least one of theavailable resource elements.
 10. The apparatus of claim 9, wherein theOFDM symbol contains a Channel State Information Reference Signal(CSI-RS).
 11. The apparatus of claim 9, wherein the precoder maintainsat least one pair of data symbols non-precoded.
 12. The apparatus ofclaim 9, wherein the precoder selects a pair of data symbols to beprecoded on a subcarrier across at least one pair of OFDM symbols. 13.An apparatus for transmitting data in a wireless communication systemusing transmission diversity, the apparatus comprising: a precoder forprecoding data symbols; a determining unit for determining, from amongresource elements in an Orthogonal Frequency Division Multiplexing(OFDM) symbol available for transmitting the precoded data symbols,whether resource elements to be mapped for transmitting the precodeddata symbols are separated by two or more indexes; a resource elementmapper for mapping the precoded data symbols to the resource elements;and a transceiver for transmitting the precoded data symbols mapped tothe resource elements, wherein, if the resource elements to be mappedfor transmitting the precoded data symbols in the OFDM symbol areseparated by two or more indexes, the precoded data symbols are notmapped to at least one of the available resource elements.
 14. Theapparatus of claim 13, wherein the OFDM symbol contains a Channel StateInformation Reference Signal (CSI-RS).
 15. The apparatus of claim 13,wherein the precoder maintains at least one pair of data symbolsnon-precoded.
 16. The apparatus of claim 13, wherein the precoderselects a pair of data symbols to be precoded on a subcarrier across atleast one pair of OFDM symbols.